As for a constant-voltage power-supply circuit, a voltage of a power-supply line is controlled to maintain a constant voltage by connecting a regulator to the power-supply line, wherein if a load circuit is short-circuited at an output side of the regulator owing to some causes, a voltage drop occurs, so that a large current flows into the regulator, causing the breakage of the regulator owing to overheat of the regulator.
To cope with such a problem, a short-circuit protective circuit is provided in the constant-voltage power-supply circuit. For example, JP 5-252649A discloses potential detection means for detecting whether the difference between an input voltage and an output voltage of a regulator exceeds a prescribed voltage wherein the output of the regulator is prohibited by controlling an output control input terminal of the regulator. Further, JP 9-34569A discloses that an output voltage is fed back to keep a transistor ON so that a regulator IC keeps its operation to maintain a stabilized output wherein if a load circuit of the output terminal is short-circuited, the voltage is not fed back to the transistor and as a result, the supply of output from the regulator IC is blocked. Still further, JP 2002-358130A discloses the function of a control circuit for turning on and off the output of a regulator IC by detecting an output voltage from an output terminal of the regulator IC.
All of the prior art references set forth above use the regulator provided with the output control terminal for a constant-voltage power-supply circuit, wherein if a voltage at an output side of the regulator drops owing to a short circuit, the voltage is fed back so as to input a stop signal to the output control terminal, thereby stopping the regulator. However, if such a circuit configuration is used for a power-supply circuit provided with a plurality of power-supply lines, the regulator has to be disposed for each power-supply line, resulting in the increase of cost. Further, even if one power-supply line is short-circuited to stop the supply of power, the remaining power-supply lines continue to supply power so that there is a possibility that the short-circuited load circuit influences upon the load circuits connected to the remaining power-supply lines. If the supply of power continues, the waste of power consumption is unavoidable.